The polyphenylene ether resins and methods for their preparation are well known in the art and described in the patent literature, including Hay, U.S. Pat. Nos. 3,306,874 and 3,036,875, which are incorporated herein by reference. Other methods of preparation are disclosed in Bennett and Cooper, U.S. Pat. Nos. 3,639,656 and 3,838,102, as well as Cooper and Bennett, U.S. Pat. Nos. 3,642,699, 3,661,848 and 3,733,299, also incorporated herein by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These processes are run in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. This has been done by the use of aqueous solutions of acetic acid, sulfuric acid, sodium bisulfate, chelating agents such as glycine, nitrilotriacetic acid and its sodium salts or ethylenediamine tetraacetic acid (EDTA) and its sodium salts. The best prior art procedure for recovery of the polyphenylene ether itself is based on precipitation from the reaction mixture with an antisolvent, i.e., a liquid which is miscible with the reaction solvent but in which the polymer does not dissolve.
By way of illustration, in producing poly(2,6-dimethyl-1,4-phenylene ether), xylenol is oxidized in toluene solution and the polymer is precipitated by addition of methanol to the reaction mixture, after removal of the copper catalyst by extraction with acids or with complexing agents such as salts of ethylenediaminetetraacetic acid, and the like. The polymer is filtered off, washed and dried. Methanol and toluene are separated by adding water to the filtrate to produce a toluene phase and a methanol-water phase almost free of toluene; toluene and methanol are then recovered by distillation.
Such procedures are not entirely satisfactory, however, because the mixture comprising the solvent for the polymer, the antisolvent for the polymer and water also contains small amounts of dissolved metal-EDTA complex and free (unchelated)EDTA salts. It is desirable to remove the metal-EDTA complex and any free EDTA salts prior to reusing the solvent and antisolvent.
This invention is based on the discovery that metal-EDTA complexes as well as free salts of EDTA can be removed, even in small amounts, from solution in a mixture of a polyphenylene ether solvent, a polyphenylene ether antisolvent and water, by contacting the mixture with a medium comprising alumina, whereby the metal-EDTA complex and free EDTA salts are selectively adsorbed on the surface of the alumina. The alumina is, moreover readily regenerated to nearly its full adsorption capacity by flushing with water at a neutral or nearly neutral pH to give an aqueous solution of the metal-EDTA complex and EDTA salts.
The use of alumina to remove various cations, among which are copper (II) and copper (II) acetylacetate, from aqueous or chlorinated hydrocarbon solutions is known. See, e.g., Chemical Abstracts, 53, 17629 g, Centini et al, Gazz. Chim. Ital., 88,607-16 (1958); and Chem. Abstracts, 58, 8534, Kavalerova et al, Zh. Fiz. Khim., 37,226-7 (1963). It has not been previously recognized, however, that EDTA-complexed metals and/or unchelated EDTA salts can be effectively removed, even in small amounts, from mixed aqueous/organic media such as those which result from conventional metal-catalyzed processes for the manufacture of polyphenylene ethers.